Twinplex telegraph signal receiver



Feb. 1, 1955 Filed June 6, 1952 H. PLETSCHER TWINPLEX TELEGRAPH SIGNAL RECEIVER 3 Sheets-Sheet 2 Q0!) fl t" I M w Q: g in: 4 l

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TWINPLEX TELEGRAPH SIGNAL RECEIVER Filed June 6, 1952 3 Sheets-Sheet 5 Volt .L' 'Qi 1NVENTOR BY ATTORNEY United States Patent G .TELEGRAPH'SIGNAL RECEIVER Hermann Pletscher, Pforzheirn, Germany, assignor to International" Standard Electric Corporation, New York, N." Y.', a' corporation of Delaware Application' June- 6', 1952, Serial. No. 292,059:

el'aimszpriority, applicationzGermany June 7, 1951 @Claimsa (CI. 178 -61) Thetwinplex' methodiisa modification'of th'e telegraphic m'ethods'that'employ the so-called keying-overto em t the marking-and spacing signals, and its use makes it possiblefor two-telegrams to be transmitted at the same time over one transmission path. t

7 While the operationof frequency keying-over consists in alternately'keying, twqfrequenciespositioned symmetrically of the nominal transmitter frequency, one frequency corresponding to the marking signal and the other torthe'spacing signal, the'twinplex method, in'its turn, emits one'or anotherof"four-'frequencies at'a time along both channels and in such a manner that each' frequency serves a.certain definite function in" respect of eithermarkingiior sp acing. These frequencies may be allotted tothe two channels A, B'as follows:v

OhannelA. Channel'B' iErequenciesu t Marking Signal." Marking Signal fl .MarkingSignaL... Spaci.ug:Signal..; L 1'2. Spacing'SignaL" 'Marking'Slgnal f3 S'paoingSignaL- spacing-signal'fln 1 f4 'by; 6000178.. Thefrequency, distances between. fliand ,r

Thetwinp'lex. receiving method. as. practised hitherto ,is as follows: .The frequencies 1, f2, f3',1f,4" areiconveyed to a two-channel converter that "comprisesan amplitude limiter,, filters to separate the. frequencies. from. each other,..,-and, signalrectifi'ers. These..rectifier s lead! toia direct current. amplifier which can at .wil1 be connected eith'ertto the'output'circuit' for channeLAlor to.thatif or channelB. Areceiving arrangement so constructed has variousrdrawbacks vizz l. The faulty impulsesin channel'B', to which the method givesriseswhen changing from one frequency to the: other, are increased. byUtheM building-up, time or transientperiod. Y

I 21 If-thielimiter. is not controlled to perfection; the filters permit the interference spectrum of their bandwidth to affect the signal rectifiers.

3. The arrangement uses a comparatively large amount of equipment, and the voice frequency filters which it employs cause the testing period to be relatively long.

The circuit arrangement which is the subject of the invention and serves to receive telegraph signals by employing, in particular, the twinplex method, is characterized in this, that the several frequencies received are conveyed to a linear converter. According to a further improvement the dilferent circuit conditions allotted to the several channels are selected by an arrangement of electron tubes.

The invention thus completely avoids the use of voice frequency filters.

2,701,276 Patented- Feb. 1-, 1955 ice One embodiment of "the invention is representeddn the accompanying drawing, in which:

Fig. 1' isafrequency arrangement that relates tome foregoing allocation table Fig. 2' 'represents the receiving circuitry;

Fig; 3 shows the converter characteristics; and

Fig: 4 illustra-tes'theanode voltage curve of the tubes employed for selection.

Ifthemark-in'ga'nd the spacing-signal frequencies are allotte'd to' the ch'annels A, B in-th'e manner herebefore explained, then it'canbeseen" from Fig. 1 that the-frequ'encies f1, f2, allotted to channel A'in respect of the m-arkingsignal, are lower than the receiving frequency fee; and that the frequencies'fS, f4, allot-ted toit in respect ofthe spacing signal, are'higher than fe. Channel A can hence be received just-as-in the case of frequency keying-over operation; the-only difference being th at for the twinplex method the markingand the spacingfrequnncies are-not in any case symmetrical with respect to e.

Thefrequencies' f1, f3, however; allotted-to channel B- inrespect of the marking signal,- are'respectivelylower and "higher thanxfe: Equally, as regards channel B; the frequencies f2; f4, fo'rthe' spacing signal, are such-that 12 is lower than fewnn'e f4 is higher than fe;

The inventi-omprovides! for selecting the signals'intended to belong tochannelA and those which are to belong t-o channel BS To-suchend the frequencies are conveyed to a li-near' converter stage.

An arrangementflsui-table'in this regard'is shown in Fig: 2." The four'tfrequencies f1, f2, f3, f4 aresupplied, after demodulation-20f the carrier, toa limiter'stag'e and th'en'ce t-O the converter-represented in Fig. 2'. The con-' linear convertedcharacteristic1 1; Fig: 3, and that 'th'edifferential voltage '-fi:on1G2," G4 results inthe li-near'converter characteristic"2, Fig- 31' In this Waythe" direct voltages-from G1'; G3, produced by'th'e frequencies-f1, f2; will be'positive while those produced-by f3, f4wil l be negative; soth'at fouch-ann'ehA, markingand spacing signals can'f' be obtainedin" the form of positiveand of nega-tive d ir'ect curren't impulses, directly from the rec'- tifiers G1;- G3? Inordentoreneratethe signals for channel-B, the second pair of rectifi'ers G2, G4 is arranged in addition to G1, G3. The direct voltages producedfby' the frequencies'fli, f4 are: positive *at' the rectifiers 1G2; G4 while those produced by: f1, fZ are' negatiVe, as -illustrated"byconverter characteristic 2; FigJ-3'. The/selection asto the circuit conditionsiallotted to -th'e-'-ch-annels," in' particul-arto channel: Bttis *rnade b'y an arrangement 'of electron tubes. The pair of rectifiers G1; G3, controls *thekeying tube R05 while :bythei pat-not rectifiers G2; G4 the' keying tube R04-isscontroliedu The -tubes' R05'-', R04 fur nish directly directacurrentaimpulses to channellB If," for instance, the circuit;con'ditionsl for the marking' 'signal"are to be utilizednto bringsaboutitheficontnolaction, the converter voltages generated by the frequencies f1, f3 must be rendered elfective. Therefore, only frequency fl is to cause anode current to flow in tube R05. To such end the grid bias source E1 is arranged to displace the converter characteristic 1, Fig. 3, into position 1'. It can thus 'be seen that only frequency f1 will be able to overcome the grid bias of R05 and thereby to actuate this tube. Tube R04 in its turn is to carry anode current when influenced by no frequency other than )3. To prevent tube R04 from becoming opened by frequency f4, tube R03 is connected in parallel with the rectifiers G2, G4 over drop resistance R3 and the control grid of R04 is biased by voltage source E2, with the result that the converter characteristic 2, Fig. 3, is displaced into po- 3 sition 2'. The grid of tube R03 is controlled by the voltage from rectifier G4. The bias source E3 for R03 is so dimensioned that the grid voltage shall be positive when the direct voltage produced by frequency I3 is exceeded by a certain amount such as bias E3. If anode current flows in tube R03, resistance R3 acts to reduce the voltage from the rectifiers G2, G4 practically to zero, so that only the negative potential of E2 will to some extent be effective at the grid of R04. No anode current can hence fiow in R04. Frequency f4 thus does not open the tube R04 and accordingly does not initiate a keying impulse. When frequency f3 produces a direct voltage from the rectifiers G2, G4, this voltage is not sufficient to overcome the bias E3 and tube R03 will not conduct. The voltage from the rectifiers G2, G4 is then sufficient to overcome the bias of E2 and tube R04 will conduct and a keying impulse is initiated. The anodes of R04, R05 are interconnected. The anode circuit thus common to them is the output circuit for channel B.

In Fig. 4 the potential on the anodes of R04, R05 is plotted in respect of the frequencies. It will be seen that decrease of the anode voltage occurs only under the influence of the frequencies f1, f3 and that accordingly only in this case marking signals are delivered to channel B. The frequencies f2, f4 do not influence the keying tubes and thus give rise to the desired spacing signals. Furthermore, the aforesaid displacement of the characteristic 1, 2, Fig 3, may be made to be such as to reduce considerably the faulty impulses arising in channel B by one frequency changing into the other. This is not possible where filters are employed.

'It is to be understood that the selecting arrangement represented in Fig. 2 is merely shown by way of example and that other selecting arrangements, or modifications of that here described, may be employed. For instance, the arrangement may be such as to provide for selecting among six or still more frequencies, which on the receiving side are brought to produce more than two circuit conditions. The invention is applicable wherever multichannel systems are operated by frequency keying-over.

What is claimed is:

1. A twinplex telegraph signal receiver comprising a linear frequency converter having a single input and first and second outputs, means for applying signal frequencies to said input at constant amplitude, first means in said converter connected to said first output for applying a direct current potential to said first output proportional to the frequency applied to said input circuit, means for applying a direct current potential to said second output when the direct current potential applied to said first output exceeds a predetermined value, second means in said converter connected to said second output for applying a direct current potential to said second output when frequencies exceeding a predetermined frequency are applied to said input circuit, and means connected to said second potential applying means and controlled thereby for preventing the application of said direct current potential to said second output when the applied frequency exceeds a predetermined greater frequency than said first predetermined frequency.

2. A twinplex telegraph signal receiver, according to claim 1, in which the converter comprises first and second tuned circuits connected to the input and tuned respectively to the lowest and the highest of the signal frequencies, an amplifier connected to each tuned circuit, first and second transformers, the primary windings of said transformers being respectively connected to the outputs of said amplifiers, first and second secondary windings on each transformer, said first windings being connected in series with the first output of said converter, said second windings being connected in series with the second output of said converter, the first potential applying means forming part of the series circuit of said first windings and comprising rectifiers so poled as to produce a direct current potential of one polarity on said first output when current flows in the first winding of said first transformer and a direct current potential of the opposite polarity when current flows in the first winding of said second transformer, the second potential applying means forming part of the series circuit of said second windings and comprising rectifiers so poled as to produce a direct current potential of one polarity on the second converter output when current fiows through said second winding of said first transformer and a direct current potential of the opposite polarity when current flows through said second winding of said second transformer.

3. A twinplex telegraph signal receiver, according to claim 2, in which the means for applying a direct current potential to the second output of the converter when the potential applied to the first output exceeds a predetermined value comprises a first electron tube with its input circuit connected to said first output, and its output circuit connected to said second output, and means for biasing said input circuit sulficiently to prevent said tube from operating when the direct current potential is below said predetermined value.

4. A twinplex telegraph signal receiver, according to claim 3, in which the second potential applying means includes a second electron tube with its output connected to the second output of the converter, and means for biasing the input of said tube to prevent its operation except when potentials exceeding a predetermined value are applied thereto.

5. A twinplex telegraph signal receiver, according to claim 4, in which the means for preventing the application of the direct current potential to the second output of the converter comprises a third electron tube connected across the input circuit of the second tube, and means for biasing the input circuit of said third tube so as to prevent the operation of said third tube unless the potential applied to the input circuit thereof exceeds a predetermined va ue.

6. A twinplex telegraph signal receiver, according to claim 1, in which the means for applying a direct current potential to the second output of the converter when the potential applied to the first output exceeds a predetermined value comprises a first electron tube with its input circuit connected to said first output and its output circuit connected to said second output, and means for biasing said input circuit sufficiently to prevent said tube from operating when the direct current potential is below said predetermined value, and in which the second potential applying means includes a second electron tube with its output connected to the second output of the converter, and means for biasing the input of said tube to prevent its operation except when potentials exceeding a predetermined value are applied thereto, and in which the means for preventing the application of the direct current potential to the second output of the converter comprises a third electron tube connected across the input circuit of the second tube, and means for biasing the input circuit of said third tube so as to prevent the operation of said third tube unless the potential applied to the input circuit thereof exceeds a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 2,464,837 Werthmann et al Mar. 22, 1949 2,543,050 Oberman Feb. 27, 1950 2,650,266 Browning Aug. 25, 1953 

